It is known to treat a bed of bulk material with gas by conveying it continuously over a grate so that the gas flows through it. To cool combustion material, for example cement clinker, it is customary to use what are known as pusher grates, which comprise overlapping rows of, in alternation, stationary grate plates and grate plates which are moved forward and back in a conveying direction (DE-A 3 734 043). The grate plates are used to blow cooling air into the bed of material, and this air is discharged above the bed of material in order for the heat to be recovered. For economic operation, pusher grates require complex mounting of the moving parts and are also complex since they are composed of relatively small parts. Another known design of grate makes use of a stationary, air-permeable supporting base, over which the layer of material is moved by means of scrapers which are moved continuously in the conveying direction or by means of reciprocating pusher members (EP-A 718 578; DE-A 10018142). The scrapers or pusher members have to be guided moveably through the grate surface from below, which is a complex arrangement. Moreover, they are exposed to high levels of wear within the hot layer of material. The passage of air is impeded and the cooling action restricted in the region of the grate in which they and their driving and sealing members are located. Yet a further type of cooler (DE-A 101 13 516) uses a large-area grate which is moved forward and back in its entirety, the bed of material being held in place by a blocker plate arranged at the start of the grate during the return stroke, so that the grate can slide beneath the blocker plate. This has the drawback that the grate length which can be utilized is limited on account of the barrier formed by the blocking action.
Working on the basis of the above prior art, the invention is based on the object of providing a method and an apparatus for treating, in particular cooling, a layer of bulk material which rests on a grate and has a stream of gas passing through it, which promise a simple structure and simple operation as well as uniform treatment of material even with a considerable grate length.